You start out with your Lantern on. Switch it off, then head forward and smash the barrels and boxes. Be sure to sneak, as there are two of those two headed zombies patrolling the next room. You can get them both in the head with the Sniper Rifle if you are quick, without either noticing. There's also some pistol bullets on the boxes that you may have already smashed. When you head forward, before you smash the wood to get to the next area, be wary of the two headed zombie on the ground. He will "wake up" when you get near, so stun him with a shock or freezing bolt before meleeing him to death, saving ammo. You can also sneak up on him and if you are quick enough, burn him with a Match. Smash the boards and walk on.
In the next room, there are two more of those two headed zombies walking around. One is on a platform that you can't get to, so it is best to get their attention, then kill them when the other is on the ground, as if he were killed when on the platform, any Green Gel or ammo he may leave behind is permanently unobtainable. When they are dead, crank on the wheel to open the gate to the other side. When it is cranked all the way up, a Key statue will come into view. Smash or shoot to obtain the key, destroy the boxes in the corner, then head on.
When you walk along this tunnel, some rocks and boards will fall from above, but this shouldn't be worried about; it is just a distraction. When you get to a stone bridge with no walls on either side, you are up for a challenge. There is an arrow machine on the left side (somewhat like the machines in Chapter 6, but not operated by any "live" enemies) that shoots harpoons along the whole length of the bridge. It starts shooting from the top, ending where you are standing. Don't walk up the bridge. Instead, crouch so you're behind the wood fence (it protects you), then dart from pillar to pillar to avoid the arrows, because they hit hard, even on Casual difficulty. There are two boxes behind a pillar that you can smash, but the arrows may destroy one for you. One of them almost always drops Gel, so time your fetching to when the barrage starts. Get across the trapped bridge in one piece, then head to the next room.
There is some pistol ammo here, and a bolt for the Agony Crossbow. When you pick up the bolt or pistol ammo, some very small creatures will spill out the board wall ahead of you. Don't bother with wasting ammo. Just run around and stomp them; they have so little health, they can even be killed by a flash bolt. Don't leave them alone, either. They can damage you by flinging themselves up into Sebastian's face, dealing minor damage. Walk to the other side of the room and listen to the audio tape on the bench nearest the door. When you start to crank on the wheel, more of those little things pour out of a fissure above your head, so stop cranking and turn them into paste under your boot. Head to the other side.
In the water, wade until you see some boards on the left side. Smash these and walk until the end, and you will find a jar of Gel and some ammo. Walk back and behind the third little waterfall is a key statue. Hop the fence and cream the little monsters, then watch out for two of those two headed zombies. There are more of the little things crawling around, so kill the big ones however you wish, then stomp the little ones, because trying to fight both types of enemies at once will most certainly net you a grapple hold and major damage from one of the large beasts. Move through the gate and then shimmy through the sliver of space in the walls.
Smash the boxes on either side, then notice the entryway with some spikes sticking out. Grab the document by the hanging guy's feet, then examine him to get the plate for the door. Unlike other puzzles in the game, this one is easy. The bloody side killed the previous attempter, so the clean side is the right side. Place the clean side in the slot and wait for the game to play the scary "did-you-do-it-right" music before it opens the door.
In the next tunnel, there are a bunch of chairs. "Waves" will pulsate down to you, so continue walking until you are deposited into a hospital hallway. Turn around to find a map fragment. Proceed forward and you'll find yourself in a cinematic. Watch the scene, and when you gain control, grab the document off the stretcher, the other one on one of the sets of machinery, and then look to the left. See all those pipes? One at the top has a key statue, so shoot it and grab the key that drops, then exit through the door.
When you do, you will be chased by a very large and grotesque monster. Run! Much like the sequence with the Keeper's traps in Chapter 7, you don't have to worry about stamina. Don't get caught on any doors that happen to be open, either. Run down the middle of the hall and Sebastian will slam the door shut behind him, blocking off the monster. Watch the scene and it is the end of the Chapter.